1. Field of the Invention
The present invention relates to a power line noise filter that reduces noise in electric power lines.
2. Description of the Related Art
Telecommunications using electric power lines, in which high frequency signals are superposed on electric power lines, is known as one of the telecommunications technologies used at home and office. During the telecommunications using electric power lines, sporadic noises of uncertain frequency bands are generated in electric power lines (hereinafter referred to as the noise) when various electric and electronic devices that are connected to the electric power lines are operated, causing higher error rates and other defects in telecommunications qualities.
A noise generated in an electric power line by operation of a device connected to the electric power line sometimes adversely affects other devices connected to the same line, even when the line is not used for telecommunications.
There are two types of noises generated in electric power lines, namely common mode noises, which propagate through two conductive lines in the same phase, and normal mode noises generated between two conductive lines. Further, noises generated in electric power lines include a noise that causes a change in electric current (hereinafter referred to as a current-related noise), and a noise that causes a change in voltage (hereinafter referred to as a voltage-related noise).
One of the measures against noise problems described above is use of a filter against electromagnetic interference (EMI) (hereinafter referred to as an EMI filter). An EMI filter is generally formed as an LC filter (a filter comprising inductors and capacitors) in which discrete elements such as a common mode choke coil, a normal mode choke coil, an X capacitor and a Y capacitor are used in combination.
Published Unexamined Japanese Patent Application (KOKAI) Heisei 7-115339 discloses a line filter that absorbs noise currents. The line filter has a first transformer including a primary coil and a secondary coil, a second transformer including a primary coil and a secondary coil, and an amplifier that amplifies a noise current that is electromagnetically induced to the secondary coil of the first transformer when the noise current flows into the primary coil of the first transformer. The noise current amplified by the amplifier is allowed to flow into the secondary coil of the second transformer to cause a change in the impedance of the primary coil of the second transformer. According to this line filter, an attenuation effect on noise is increased through adjustment of the impedance of the primary coil of the second transformer.
Published Unexamined Japanese Patent Application (KOKAI) Heisei 10-303674 discloses an AC line filter that reduces noise in an AC power source line. The AC line filter comprises: a common mode choke coil to which a third winding has been added; a noise extraction circuit that extracts common mode noise in the AC power source line; a noise amplifying circuit that amplifies the extracted common mode noise; and an electric current supplying circuit that supplies a current for providing an electromotive force of inverted phase to the third winding of the common mode choke coil in response to outputs of the noise amplifying circuit. According to this AC line filter, the noise extraction circuit extracts common mode noise in the AC power source line, the noise amplifying circuit amplifies the extracted common mode noise, and, in response to the outputs of the noise amplifying circuit, the electric current supplying circuit supplies a current for providing an electromotive force of inverted phase to the third winding of the common mode choke coil. Common mode noise in the AC power source line are thereby reduced.
Conventional EMI filters formed as an LC filter are advantageous in that the circuits can be easily configured, but on the other hand they have drawbacks such as (1) to (3) described below.
(1) Conventional EMI filters can provide a desired attenuation amount only within a narrow frequency band, because those filters have specific resonance frequencies that depend on inductance and capacitance.
(2) EMI filters need to be optimized according to devices that generate noises, because frequency bands, intensity and characteristics of noises generated differ among electric/electronic devices. Thus, a process of trial and error is required each time a device is designed, to optimize EMI filters so that they are compatible with the standards related to noises, which in turn necessitates a long time for measurements and evaluations, and makes standardization of EMI filters difficult.
(3) Since conventional EMI filters can provide a desired attenuation amount only within a narrow frequency band, their noise reduction effect fluctuates due to variations in noise frequencies among different noise sources and differences in attenuation characteristics among EMI filters.
According to the line filter disclosed in Published Unexamined Japanese Patent Application (KOKAI) Heisei 7-115339, the impedance of the primary coil of the second transformer is adjusted by allowing currents which synchronize after a lapse of one cycle with the noise currents detected by the first transformer to flow into the secondary coil of the second transformer. Therefore, this line filter may be effective for reducing continuous noise with a constant frequency, but it is not capable of canceling sporadic noise. FIG. 4 in this reference shows an example of the line filter configuration in which a line is passed around two cores together, with the secondary coil of the first transformer and the secondary coil of the second transformer being wound around the cores respectively. In this configuration, however, the two cores can easily become misaligned, and cabling would be difficult.
According to the AC line filter disclosed in Published Unexamined Japanese Patent Application (KOKAI) Heisei 10-303674, as shown in FIGS. 1 and 2 thereof, common mode noise is detected by detecting variations in voltage in a neutral line through the use of a high path filter (HPF), and the detected common mode noise is amplified by the noise amplifying circuit. Then, in response to outputs of the noise amplifying circuit, the electric current supplying circuit generates a current for providing the third winding of the common mode choke coil with an electromotive force of inverted phase, and supplies the current to the third winding of the common mode choke coil.
Thus, in the above AC line filter, the voltage of the common mode noise (hereinafter referred to as the noise voltage) is detected, and the noise voltage is amplified and then converted into a current having a phase inverted to that of the common mode noise (hereinafter referred to as a phase-inverted current), so as to cancel the common mode noise using the phase-inverted current.
In the above AC line filter, however, a delay of the phase-inverted current against the noise voltage occurs during the processes of amplifying the noise voltage and converting the noise voltage into the phase-inverted current. Further, waveform of the noise voltage and that of the phase-inverted current do not coincide with each other completely. For these reasons, it is difficult to accurately cancel common mode noise in AC power source lines using the above AC line filter.
Basically, the above AC line filter reduces common mode noise using the common mode choke coil, and, enhances the effect of reducing common mode noise by supplying the phase-inverted current to the third winding of the common mode choke coil. Therefore, it is difficult for this AC line filter to reduce noise over a wide frequency band, because its attenuation characteristics depend on the properties of the common mode choke coil.
Further, in the above AC line filter, the HPF for extracting common mode noise is provided between the neutral line and the frame ground, and the third winding for canceling the common mode noise is connected between the frame ground and the electric current supplying circuit. Therefore, the AC line filter would not function when there is no frame ground, and further it is capable of canceling only the common mode noise generated between the frame ground and the neutral line. In other words, this AC line filter is applicable in extremely limited fields.
FIG. 5 of Published Unexamined Japanese Patent Application (KOKAI) Showa 53-54447 shows a filter that blocks carrier waves propagated through an electric power line. The filter has a pair of inputs, a pair of outputs, a parallel resonant circuit placed between one of the inputs and one of the outputs, and a serial resonant circuit placed between the two outputs. According to the parallel resonant circuit of this filter, on the magnetic core, a magnetic flux of a commercial current superposed with high frequency signals is canceled with a magnetic flux of a commercial current from which high frequency signals have been removed with a low-range passage filter, to thereby make impedance larger with respect to the high frequency signals. The principle for blocking carrier waves by this filter differs completely from the principle of noise reduction by a power line noise filter according to the invention detailed later.
It is an object of the invention to provide a power line noise filter that can effectively reduce noise in electric power lines over a wide frequency band, and can also effectively reduce sporadic noise as well as continuous noise.
A first power line noise filter according to the invention comprises:
a noise detection circuit (noise detection means) for detecting a noise in an electric power line by detecting variations in electric current in the electric power line;
a phase-inverted signal generation circuit (phase-inverted signal generation means) for generating a phase-inverted signal whose phase is inverted to that of the noise detected by the noise detection circuit (noise detection means); and
a noise cancellation circuit (noise cancellation means) for canceling the noise in the electric power line by causing a change in electric current in the electric power line, the change corresponding to the phase-inverted signal generated by the phase-inverted signal generation circuit (phase-inverted signal generation means).
In the first power line noise filter of the invention, the noise detection circuit (noise detection means) detects noise in an electric power line by detecting variations in electric current in the power line. Then, the phase-inverted signal generation circuit (phase-inverted signal generation means) generates a phase-inverted signal whose phase is inverted to that of the noise detected by the noise detection circuit (noise detection means). Further, the noise cancellation circuit (noise cancellation means) causes a change in electric current in the power line, the change corresponding to the phase-inverted signal, and thereby cancels the noise in the power line.
In the first power line noise filter of the invention, the noise detection circuit (noise detection means) may detect noises propagating through two conductive lines of the electric power line in the same phase, and the noise cancellation circuit (noise cancellation means) may cause the same changes in electric current for the two conductive lines of the electric power line.
Further, in the first power line noise filter of the invention, the noise detection circuit (noise detection means) may detect noise occurring in each of two conductive lines of the electric power line, separately for each of the conductive lines; the phase-inverted signal generation circuit (phase-inverted signal generation means) may generate the phase-inverted signals separately for the two conductive lines, the phase-inverted signals respectively corresponding to the noises detected for the two conductive lines by the noise detection circuit (noise detection means); and the noise cancellation circuit (noise cancellation means) may cause changes in electric current separately for the two conductive lines of the electric power line, the changes respectively corresponding to the phase-inverted signals generated for the two conductive lines by the phase-inverted signal generation circuit (phase-inverted signal generation means).
A second power line noise filter according to the invention comprises:
a noise detection circuit (noise detection means) for detecting a noise in an electric power line by detecting variations in voltage in the electric power line;
a phase-inverted signal generation circuit (phase-inverted signal generation means) for generating a phase-inverted signal whose phase is inverted to that of the noise detected by the noise detection circuit (noise detection means); and
a noise cancellation circuit (noise cancellation means) for canceling the noise in the electric power line by causing a change in voltage in the electric power line, the change corresponding to the phase-inverted signal generated by the phase-inverted signal generation circuit (phase-inverted signal generation means).
In the second power line noise filter of the invention, the noise detection circuit (noise detection means) detects noise in an electric power line by detecting variations in voltage in the power line. Then, the phase-inverted signal generation circuit (phase-inverted signal generation means) generates a phase-inverted signal whose phase is inverted to that of the noise detected by the noise detection circuit (noise detection means). Further, the noise cancellation circuit (noise cancellation means) causes a change in voltage in the power line, the change corresponding to the phase-inverted signal, and thereby cancels the noise in the power line.
In the second power line noise filter of the invention, the noise detection circuit (noise detection means) may detect noises propagating through two conductive lines of the electric power line in the same phase, and the noise cancellation circuit (noise cancellation means) may cause the same changes in voltage for the two conductive lines of the electric power line.
Further, in the second power line noise filter of the invention, the noise detection circuit (noise detection means) may detect noise occurring in each of two conductive lines of the electric power line, separately for each of the conductive lines; the phase-inverted signal generation circuit (phase-inverted signal generation means) may generate the phase-inverted signals separately for the two conductive lines, the phase-inverted signals respectively corresponding to the noises detected for the two conductive lines by the noise detection circuit (noise detection means); and the noise cancellation circuit (noise cancellation means) may cause changes in voltage separately for the two conductive lines of the electric power line, the changes respectively corresponding to the phase-inverted signals generated for the two conductive lines by the phase-inverted signal generation circuit (phase-inverted signal generation means).
A third power line noise filter according to the invention comprises:
a first noise detection circuit (first noise detection means) for detecting a first noise in an electric power line by detecting variations in electric current in the electric power line;
a first phase-inverted signal generation circuit (first phase-inverted signal generation means) for generating a first phase-inverted signal whose phase is inverted to that of the first noise detected by the first noise detection circuit (first noise detection means);
a first noise cancellation circuit (first noise cancellation means) for canceling the first noise in the electric power line by causing a change in electric current in the electric power line, the change corresponding to the first phase-inverted signal generated by the first phase-inverted signal generation circuit (first phase-inverted signal generation means);
a second noise detection circuit (second noise detection means) for detecting a second noise in the electric power line by detecting variations in voltage in the electric power line;
a second phase-inverted signal generation circuit (second phase-inverted signal generation means) for generating a second phase-inverted signal whose phase is inverted to that of the second noise detected by the second noise detection circuit (second noise detection means); and
a second noise cancellation circuit (second noise cancellation means) for canceling the second noise in the electric power line by causing a change in voltage in the electric power line, the change corresponding to the second phase-inverted signal generated by the second phase-inverted signal generation circuit (second phase-inverted signal generation means).
In the third power line noise filter of the invention, the first noise detection circuit (first noise detection means) detects the first noise in an electric power line by detecting variations in electric current in the power line. Then, the first phase-inverted signal generation circuit (first phase-inverted signal generation means) generates the first phase-inverted signal whose phase is inverted to that of the first noise detected by the first noise detection circuit (first noise detection means). Then, the first noise cancellation circuit (first noise cancellation means) causes a change in electric current in the power line, the change corresponding to the first phase-inverted signal, and thereby cancels the first noise in the power line. Further, the second noise detection circuit (second noise detection means) detects the second noise in the electric power line by detecting variations in voltage in the power line. Then, the second phase-inverted signal generation circuit (second phase-inverted signal generation means) generates the second phase-inverted signal whose phase is inverted to that of the second noise detected by the second noise detection circuit (second noise detection means). Then, the second noise cancellation circuit (second noise cancellation means) causes a change in voltage in the power line, the change corresponding to the second phase-inverted signal, and thereby cancels the second noise in the power line.
In the third power line noise filter of the invention, the first noise detection circuit (first noise detection means) may detect first noises propagating through two conductive lines of the electric power line in the same phase; the first noise cancellation circuit (first noise cancellation means) may cause the same changes in electric current for the two conductive lines of the electric power line; the second noise detection circuit (second noise detection means) may detect second noises propagating through two conductive lines of the electric power line in the same phase; and the second noise cancellation circuit (second noise cancellation means) may cause the same changes in voltage for the two conductive lines of the electric power line.
In the third power line noise filter of the invention, the first noise detection circuit (first noise detection means) may detect the first noise occurring in each of two conductive lines of the electric power line, separately for each of the conductive lines; and the first phase-inverted signal generation circuit (first phase-inverted signal generation means) may generate the first phase-inverted signals separately for the two conductive lines, the first phase-inverted signals respectively corresponding to the first noises detected for the two conductive lines by the first noise detection circuit (first noise detection means); the first noise cancellation circuit (first noise cancellation means) may cause changes in electric current separately for the two conductive lines of the electric power line, the changes respectively corresponding to the first phase-inverted signals generated for the two conductive lines by the first phase-inverted signal generation circuit (first phase-inverted signal generation means); the second noise detection circuit (second noise detection means) may detect the second noise occurring in each of two conductive lines of the electric power line, separately for each of the conductive lines; the second phase-inverted signal generation circuit (second phase-inverted signal generation means) may generate the second phase-inverted signals separately for the two conductive lines, the second phase-inverted signals respectively corresponding to the second noises detected for the two conductive lines by the second noise detection circuit (second noise detection means); and the second noise cancellation circuit (second noise cancellation means) may cause changes in voltage separately for the two conductive lines of the electric power line, the changes respectively corresponding to the second phase-inverted signals generated for the two conductive lines by the second phase-inverted signal generation circuit (second phase-inverted signal generation means).
A fourth power line noise filter of the invention comprises:
a noise detection circuit (noise detection means), provided at a specific position on an electric power line, for detecting noise in the electric power line by detecting variations in electric current or voltage in the electric power line;
a phase-inverted signal generation circuit (phase-inverted signal generation means) for generating a phase-inverted signal whose phase is inverted to that of the noise detected by the noise detection circuit (noise detection means);
a noise cancellation circuit (noise cancellation means), provided at a position on the electric power line different from that of the noise detection circuit (noise detection means), for canceling the noise in the electric power line by causing a change in electric current in the electric power line corresponding to the phase-inverted signal generated by the phase-inverted signal generation circuit (phase-inverted signal generation means), in the case where the noise detection circuit (noise detection means) detects the noise by detecting variations in electric current in the electric power line; or by causing a change in voltage in the electric power line corresponding to the phase-inverted signal generated by the phase-inverted signal generation circuit (phase-inverted signal generation means), in the case where the noise detection circuit (noise detection means) detects the noise by detecting variations in voltage in the electric power line; and
a peak-value-reducing impedance component that is provided between the noise detection circuit (noise detection means) and the noise cancellation circuit (noise cancellation means) on the electric power line, and has an impedance that reduces a peak value of a noise passing therethrough.
In the fourth power line noise filter of the invention, the noise detection circuit (noise detection means) detects noise in an electric power line by detecting variations in electric current or voltage in the power line. Then, the phase-inverted signal generation circuit (phase-inverted signal generation means) generates a phase-inverted signal whose phase is inverted to that of the noise detected by the noise detection circuit (noise detection means). Then, the noise cancellation circuit (noise cancellation means) causes a change in electric current or voltage in the power line, the change corresponding to the phase-inverted signal. Further, in this noise filter, the peak-value-reducing impedance component reduces the peak value of noise on the noise-cancellation-circuit(means)-side of the power line, and, keeps a difference in peak value between the noise on the noise-detection-circuit(means)-side of the power line and the noise on the noise-cancellation-circuit (means)-side of the power line.
In the fourth power line noise filter of the invention, the peak-value-reducing impedance component may include an inductor.
The fourth power line noise filter of the invention may further comprise a phase-adjusting impedance component, the impedance component being provided along a signal path starting from the noise detection circuit (noise detection means) to reach the noise cancellation circuit (noise cancellation means) via the phase-inverted signal generation circuit (phase-inverted signal generation means), and having an impedance that adjusts a phase of the phase-inverted signal such that a phase difference between the noise inputted to the noise cancellation circuit (noise cancellation means) and the change in electric current or voltage in the electric power line caused by the noise cancellation circuit (noise cancellation means) is made closer to 180xc2x0. In this case, the phase-adjusting impedance component may include an inductor.
Other and further objects, features and advantages of the invention will appear more fully from the following description.